1. Field of the Invention
The present invention relates to a silicon etching method, and more particularly, to a silicon etching method using a plasma.
2. Description of the Related Art
A trench etching that forms a groove-shaped trench for isolation of elements or a cylindrical trench for capacitors is a representative silicon (Si) etching. A trench etching method of forming deep trenches for deep trench isolation (DTI) and a trench etching method of forming trenches for memory cells and capacitors form trenches with widths in the range of about 0.8 to about 1.2 μm and depths in the range of about 5 to about 8 μm in a major surface of a Si substrate. Those trench etching methods are representative trench etching methods of forming trenches with large aspect ratios. Recent three-dimensional IC devices and micro electromechanical systems (MEMSs) require an etching method capable of forming wiring through holes and trenches with depths not smaller than 100 μm for mechanical structures in a Si substrate.
Most conventional Si etching methods use a SF6/O2 mixed gas as a reactive gas for producing a reactive plasma. A SF6 gas derived plasma contains F atoms in a F atom density several times those of plasmas derived from other fluorinated gases, and S atoms of SF6 prevents the oxidation of the surface of Si substrate and promotes Si etching. Thus, it is considered that SF6 gas is an optimum etching gas for etching the Si substrate at a high etch rate. Oxygen gas (O2 gas) reacts with Si of the Si substrat , forms oxide films (SiOx films) on sidewalls, and promotes vertical (anisotropic) etching.
The sidewall protecting effect of the SF6/O2 mixed gas in Si etching is not satisfactory. Consequently, undercuts or encroachments are liable to be formed in the side walls of the etched holes or grooves and it is difficult to achieve vertical (anisotropic) etching. Moreover, the SF6/O2 mixed gas is unsatisfactory in the etch selectivity of Si with respect to the masking material (hereinafter referred to as “Si etch selectivity”), and can etch in a limited depth.
In order to make up for the shortcomings of the SF6/O2 mixed gas, an etching method that performs an etching cycle using the SF6/O2 mixed gas and a deposition cycle using a CFx gas alternately has been proposed. However, processing efficiency or throughput of this etching method is low because etching does not progress during the deposition cycle.